A bit of a beast (5)

I believe the answer is:

hippo

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'beast' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for hippo that I've seen before include "African river mammal" , "Large animal" , "Water-loving mammal" , "large African creature" , "Tropical African mud wallower" .)

I've seen this clue in the Evening Standard.

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